From the ESL Student Handbook, by Young Min, PhD

A thesis statement refers to the main argument in your paper. Different cultures have different ways of developing a thesis statement in writing: some Asian writers are trained to present the main argument of their paper toward the end of the main body, just before the conclusion. In English, however, you are supposed to present your thesis at the beginning of the paper (toward the end of your introduction) and develop your argument by presenting supporting details in the body of your paper. Thus, it is critical for you to learn ways to construct a clear thesis statement and develop your argument as effectively as possible. Here are some tips you should remember when you construct a thesis statement in your paper.
Write your thesis statement in a complete sentence rather than in a phrase.

This paper examines how listening to classical music can improve students’ concentration when they study for exams. (Thesis statement)

Express the main point of your argument or your point of view rather than just introducing the topic of your paper.

I am going to discuss the effects of yoga on the human body. (Not a thesis statement)

In this paper, I am going to discuss positive aspects of yoga on the human body based on my own experience of doing yoga during my rehabilitation training. (Thesis statement)

This paper examines positive effects of doing yoga on the human body based on my personal experience as well as published studies. (Thesis statement)

Express a clear point of view rather than stating just a fact that everybody already knows.

Eating fresh vegetables is good for our health. (Not a thesis statement)

Although eating vegetables is good for our health, recent studies highlight that overeating vegetables can also cause serious implications to our health. (Thesis statement)

This paper discusses the importance of eating the right amount of vegetables each meal based on James Brown’s 2009 study. (Thesis statement)

Present your opinion or an idea that needs to be developed or proved to your audience, rather than stating a general idea that is too vague or too large of a topic to be adequately covered in an essay.

There are many advantages and disadvantages of living in an apartment. (Not a thesis statement)

As the economic depression has brought many problems these days, I strongly believe that the advantages of living in an apartment outweigh the disadvantages. (Thesis statement)

This paper examines the advantages of living in an apartment based on the recent studies conducted by Sandra Smith and David Edwards in 2007. (Thesis statement)

Express only one idea about one topic in your thesis statement.

Talking to your friends during study is important, and I have found that studying in a coffee shop rather than a library is a better option. (Not a thesis statement)

Studying in a coffee shop can be more effective than studying in a library since it can foster a lively conversation about course assignments with other people. (Thesis statement)

This paper looks into positive aspects of studying in a coffee shop based on my own experience as well as published studies. (Thesis statement)